An activist daubs graffiti on the Basque County tourist board in Bilbao

Rafael Gallego, chair of the Spanish Association of Travel Agents (Feaav), branded the protesters “fascists” and said their actions could get worse.

He said: “This tourismphobia has been worrying us since last summer. In 2016 we noted graffiti and there was an aggression with a glass against tourists who were on an excursion, so we alerted that the situation could radicalise, which is what we have seen.

“Now there are protests in the entrances of hotels, restaurants and in ports.

Rafael Gallaleo, the head of the Spanish Association of Travel Agents, branded the protesters “fascists” and said the spate of “tourismphobia” started last summer. Pictured, another protester spray painting a message on the Basque County tourist board

This summer four hooded activists from a radical group called Arran attacked a tourist bus in Barcelona, slashing tyres and spraying slogans across it.

Others have thrown eggs at hotels, and there have been demonstrations around the city’s famous Sagrada Familia basilica.

In Palma, Majorca, they set off smoke flares outside a seafront restaurant, while in Bilbao, northern Spain, another group sprayed paint across the headquarters of the Basque Country tourist board on Wednesday.

The groups claim tourism is destroying Spanish cities, driving up rent and forcing out young people.

Laura Flores, 24, one of the leaders of the group, called Arran, told The Times: “We cannot rule out more attacks. There have been assaults in the past and there will be more in the future.” Pictured, protesters fire flares and hold signs by a port

Arran also attacked tourists on a sightseeing bus in Barcelona. The militant group entered a restaurant in Palma de Majorca and threw confetti at frightened diners

In Barcelona, where anger has been brewing for some time, tourists thought they were under attack from terrorists this week, when masked men attacked their open top bus.

Laura Flores, 24, one of the leaders of the group, called Arran, told The Times: “We cannot rule out more attacks. There have been assaults in the past and there will be more in the future.”

The group says that mass tourism is spoiling Spain, and pushing locals out by driving up rental prices.

Even graffiti in the city has turned menacing with one slogan, featuring a black silhouette with a red target on its head, reads: "Why call it tourist season if we can't shoot them?"

There is concerns that the violence could spread.

A video emerged of masked Arran activists setting off flares outside a restaurant full of tourists on the island of Palma de Majorca. They then entered the restaurant and threw confetti at frightened diners.

In Venice last month, residents marched through a throng of visitor to protest against uncontrolled tourism. They did so behind a banner: "My future is Venice".

Of the protests in Spain, a spokesman for the Foreign Office said: “We are aware and monitoring the situation. We are also in contact with the local authorities. There is no specific update to our travel guidance but we keep it under constant review.”

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